Refrigeration Insights Series. Season 3: The IIAR Standards, installment 3 of 10.
In an industrial refrigeration system there are hundreds of valves. Each one is a boundary: between high and low pressure, between a section that can be worked on and one that cannot, between normal operation and a leak. That is why the most repeated component in the system has an entire standard of its own: ANSI/IIAR 3-2022, Ammonia Refrigeration Valves.
What IIAR 3 is
Its purpose, in one line: to specify performance criteria for valves and strainers used in closed-circuit ammonia refrigeration systems.
It is a product standard, not an installation standard. While IIAR 2 speaks to the engineer who designs the system and IIAR 4 to the contractor who erects it, IIAR 3 speaks above all to the manufacturer: it defines what a valve has to meet in order to be called an ammonia refrigeration valve.
Which components it covers
The scope includes stop valves, control valves, check valves, ball valves, gauge valves, butterfly valves and strainers, designed and manufactured for closed-circuit mechanical ammonia refrigeration systems.
For each family, the standard sets criteria on materials of construction, the pressure-containing envelope, allowable seat leakage, quality assurance, marking and production testing.
That last point is key for the buyer: a valve conforming to IIAR 3 arrives marked and factory tested. The marking is the traceability that any mechanical integrity audit will later ask for.
Two acronyms you need to master
The standard precisely defines two concepts that are often confused:
MAWP (Maximum Allowable Working Pressure). The maximum allowable working pressure for which the equipment, component or device was designed. It is a design limit: it defines the mechanical boundary of the valve.
MOPD (Maximum Operating Pressure Differential). The maximum operating pressure differential against which the valve can operate. It is a functional limit: a solenoid valve can withstand the system pressure and still be unable to open if the differential exceeds its MOPD.
Buying a valve looking only at the MAWP and forgetting the MOPD is a classic that ends in valves that do not open when they are needed most.
A standard that does not work alone
IIAR 3 is always read together with its normative references: IIAR 1 for definitions, IIAR 2 for the system design context, and ASME B31.5 for the refrigeration piping and heat transfer components those valves are welded or threaded to.
In practice, the circuit goes like this: IIAR 2 tells you where a valve goes and what for; IIAR 3 tells you what that valve has to meet as a product; IIAR 4 tells you how to install it; and IIAR 6 will tell you how to maintain it for the next twenty years.
What changed from 2017
The 2022 edition replaces the 2017 edition within the five-year review cycle that ANSI requires for all IIAR standards: each standard is reviewed at least every five years, with a public review period in which any interested party can propose changes. That consensus process is what makes these standards a reference outside the United States as well.
The practical advice
When you put together your next valve order, add one line to the specification: "conforming to ANSI/IIAR 3-2022, with marking and production testing per the standard". Those few words save you arguments with the supplier and leave you the documentary backing that audits will ask for.
Next week: IIAR 4, the installation standard, where the best design can be ruined or consolidated.
Source: ANSI/IIAR 3-2022, Ammonia Refrigeration Valves, International Institute of Ammonia Refrigeration. Thermomac is a corporate member of the IIAR.
